Contoured Package-on-Package Joint

ABSTRACT

A contoured package on package joint and a method for making the same are disclosed herein. A method for forming a device comprises providing a substrate having a package land and forming a mounting stud on the package land. A molded underfill is applied to the substrate and in contact with the mounting stud. A contoured stud surface is formed on the mounting stud is contoured and connecting member attached to the contoured stud surface with a second package attached to the connecting member. The connecting member may be solder and have a spherical shape. The contoured stud surface may be etched or mechanically formed to have a hemispherical shape conforming to the connecting member shape.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. These smallerelectronic components also, in some instances, require smaller packagesthat utilize less area than packages of the past.

Package on package (PoP) technology is becoming increasingly popular forits ability to allow denser integration of integrated circuits into asmall overall package. PoP technology is employed in many advancedhandheld devices, such as smart phones. While PoP technology has allowedfor a lower package profile, the total thickness reduction is currentlylimited by the solder ball joint height and the distance betweenadjacent joints, referred to as the pitch. Dies are sometimes mounted toan interposer substrate or other packaging carrier via a mountingconductor such as a ball grid array, land grid array, pin array, or thelike. In some instances, an undermount filler or underfill may beapplied between the die and the interposer PC board to fill the spacesbetween the mounting conductors.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flow diagram illustrating a method for forming apackage-on-package device with contoured mounting studs according to anembodiment of the disclosure;

FIGS. 2 through 9 illustrate cross-sectional views of intermediate stepsin forming a package-on-package device with contoured mounting studsaccording to an embodiment of the disclosure;

FIGS. 10 through 15 illustrate cross-sectional views of intermediatesteps in forming of a package-on-package device with contoured mountingstuds according to a second embodiment of the disclosure;

FIGS. 16A-16B illustrate cross-sectional views of contoured mountingstuds according to embodiments of the disclosure; and

FIG. 17 illustrates a cross-sectional view of embodiments of contouredpackage-on-package joints according to an embodiment of the disclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to illustrate the relevant aspects of the embodiments and are notnecessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that thepresent disclosure provides many applicable concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the disclosure, and do not limit the scope of the disclosure.Note that, for simplification, not all element numbers are included ineach subsequent drawing. Rather, the element numbers most pertinent tothe description of each drawing are included in each of the drawings.

FIG. 1 is a flow diagram illustrating a method 100 for forming apackage-on-package device with contoured mounting studs according to anembodiment of the disclosure, and is described in conjunction with FIGS.2 through 9, which illustrate cross-sectional views of intermediatesteps the embodiment of the method 100 of FIG. 1.

Referring now to FIG. 1, a first substrate 200 is provided in block 102,as shown in FIG. 2. The first substrate 200 may comprise an interposersubstrate 208 having one or more through vias 210, one or more die lands206, one or more package lands 202, and one or more mounting lands 212.While a single first substrate 200 is shown in the drawings, severalfirst substrates 200 may optionally be processed on a workpiece (notshown) comprising a plurality of first substrates 200, and the workpiecemay be singulated during a subsequent process step.

The interposer substrate 208 may have one or more redistribution layers(RDLs) 216, 218 disposed on one or both sides of the interposersubstrate 208. The interposer substrate 208 through vias 210 maycomprise conductive material connecting the first RDL 216 at the firstside 200 a of the first substrate 200 to the second RDL 218 at thesecond side 200 b of the substrate. The RDLs 216 and 218 may comprisedielectric layers with one or more mounting pads or lands 202, 206 and212 which may be electrically connected to the through vias 210 and eachwith at least one surface exposed through the surface of the RDLs 216and 218. For example, the first RDL 216 may have one or more packagelands 202 configured for mounting a second package 902 (not shown inFIG. 2, see FIG. 9) or one or more die lands 206 configured for mountingone or more dies 602 (not shown in FIG. 2, see FIG. 6) on the first RDL216. The second RDL 218 may have one or more mounting lands 212 formounting the completed package-on-package device 900 (not shown in FIG.2, see FIG. 9) to a PCB, to another package or device, or the like.

In some embodiments, the first substrate 200 may optionally comprise apassivation layer 204 or other protective layer disposed on the firstRDL 216. The passivation layer 204 may be an oxide, a nitride, ananticorrosion coating, or another suitable coating. The passivationlayer may lie over the package lands 202, or may be formed withopenings, for example, with opening over the die lands 206.

The stud pads or mounting lands 202 maybe masked in block 104, asillustrated in FIG. 3. A mask 302 may be formed from material such as aspin-on photoresist, a hard mask, or the like to form a mask 302. Themask 302 may be patterned, for example, by exposure and development of aphotoresist mask 302. In another embodiment, a hard mask 302 may beused. In such an embodiment, a hard mask 302 material, such as nitridelayer, for example, may be deposited, patterned and etched to result ina patterned hard mask 302.

The passivation layer 204 may be etched in block 106, as illustrated inFIG. 4. Patterning the mask 302 may result in one or more stud openings402 formed in the mask. The passivation layer etching of block 106 maybe omitted, for example, where a passivation layer 204 is absent, orwhere the passivation layer 204 is formed with openings over the packagelands 202.

Mounting studs 502 may be formed on the package lands 202 in block 108,and as shown in FIG. 5. The mounting studs 502 may be disposed on, andin electrical contact with the package lands 202. In one embodiment, themounting studs 502 may be formed through a deposition process such aselectroplating, plasma enhanced vapor deposition, chemical vapordeposition, physical vapor deposition, sputtering, or another process.In another embodiment, the mounting studs 502 may be formed separatelyfrom the first substrate 200 and then placed on the package lands 202.

The mounting studs 502 may be formed of any suitable conductivematerial, for example, copper, gold, tungsten, aluminum, alloys of anyof the same, conductive polymers, or the like. In some embodiments, themounting studs 502 will have a melting point greater than that ofsolder, and may also have a structural rigidity sufficient to supportmounting of a second package 902 (see FIG. 9).

The mounting studs 502 may also be formed to a predetermined height, andin one embodiment, may be formed to have a top surface about level withthe top surface 302 a of the mask 302. In another embodiment, themounting studs 502 may be formed to have a top surface below the topsurface 302 a of the mask 302.

The mask may be removed in block 110 and a die 602 mounted on the firstsubstrate 200 in block 114. FIG. 6 illustrates the first substrate 200after removing the mask 302 (see FIG. 5) and after mounting the die 602.One or more dies 602 may be mounted on the die lands 206. While themounting of a single die 602 is illustrated for clarity, any number ofdies 602 may be mounted to the die lands 206. The die 602 may, in someembodiments, be mounted to the die lands 206 via solder balls in a ballgrid array, via surface mount technology, pin grid arrays, wireinterconnects, conductive adhesive, a socket, or another suitabletechnique.

A molded underfill (MUF) 702 maybe applied in block 116, as shown inFIG. 7. The MUF 702 may fill the area under the die 602 and the areaaround the package lands 202. In some embodiments, the MUF 702 may be anonconductive material, and may be an epoxy, a resin, a moldablepolymer, or the like. The MUF 702 may be applied while substantiallyliquid, and then may be cured through a chemical reaction, such as in anepoxy or resin. In other embodiments, the MUF 702 may be an ultraviolet(UV) or thermally cured polymer applied as a liquid, gel or malleablesolid.

In one embodiment, a mold may be provided to retain and shape the MUF702 during application and curing. For example, a mold may have a borderor other feature for retaining the MUF 702 material when applied. Themold may optionally further comprise a release film to assist in partingthe mold from the MUF 702. The optional release film may be used inembodiments where the MUF 702 is an epoxy or resin to prevent the MUF702 material from adhering to the mold surface.

In one embodiment, the MUF 702 may be applied to have a top surface 702a below, or lower than the top surface 602 a of the die 602.Additionally, the MUF 702 may have a top surface 702 a exposing a topportion of the mounting studs 502. In another embodiment, the MUF 702may be formed over the top surface 602 a of the die 602, or over the topsurfaces of the mounting studs 502, and may be reduced via polishing orgrinding to expose a portion of the mounting studs 502.

The mounting studs 502 may be contoured in block 118, as shown in FIG.8. A first package 800 having contoured mounting studs 502 is thusformed. In one embodiment, a contoured stud surface 802 may be formed atthe top of the mounting stud 502, and may accept a connecting member 904(not shown, see FIG. 9) to attach a second package 902 (FIG. 9).

The mounting studs 502 may be contoured using chemical means, mechanicalmeans, or via another suitable procedure. For example, in oneembodiment, the mounting studs 502 may be copper, and may be etched withferric chloride (FeCl₃) or a copper chloride (CuCl₂) and hydrochloricacid (HCl) solution. A spray or vapor etching environment may permitetching of a generally hemispherical contoured stud surface 802. Theconcentrations of etchant and etching conditions may be predetermined toresult in a contoured stud surface 802 having a radius and depthcalculated to accept a complementary connecting member 904 of apredetermined size. For example, a directed spray etch may direct agreater amount of etchant to the center of the mounting stud 502 to etchthe center of the mounting stud 502 to a greater depth. Additionally,one or more contact masks or non-contact stencils may be used to maskall or part of the mounting stud surface during, for example, a sprayetch. In such an embodiment, an etchant spray may be directed through anon-contact stencil with an opening smaller than the cross section ofthe mounting stud 502, and the spray may diffuse across the surface ofthe mounting stud, but be primarily directed to the center of themounting stud to etch to etch the center of the mounting stud 502 to agreater depth. One embodiment may be where a series of contact masks areapplied to the mounting stud to permit etching to a greater depth at thecenter of the mounting stud 502.

In another embodiment, the contoured stud surface 802 may bemechanically created by a process such as milling, drilling, abrasiveremoval or cutting. For example, a ball end mill having a predeterminedradius may be used to mill the mounting stud 502 to create the desiredtopography for the contoured stud surface 802. Alternatively, thecontoured stud surface 802 may be created by abrasive blasting orabrasive grinding.

A second package 902 may be mounted to the first package 800 in block120, resulting in a package-on-package device 900 shown in FIG. 9. Aconnecting member 904 may be used to connect the second package 902 tothe first package 800.

In some embodiments, the second package 902 may have an interposersubstrate 208 with one or more vias 210 disposed therein. The interposersubstrate 208 may the same material as the first substrate 200interposer substrate 208, or may be a different material. In someembodiments, one or more second dies 908 may be mounted to the secondpackage 902 by way of an adhesive or other mounting technique. Thesecond dies 908 may be electrically connected to one or more via lands910 in the interposer substrate 208 via a wire bond 912. In otherembodiments, the second dies 908 may be mounted to the second package902 interposer substrate 208 via a ball grid array, via a socket, viasurface mounting technology, or the like. The second dies 908 may be inelectrical communication with the first package 800 by way of theconnecting member 904, the mounting studs 502, and the package lands202.

In some embodiments, the connecting members 904 may be solder ballsapplied to via lands 910 connected to vias 210 in the interposersubstrate and exposed at both sides of the second package 902.Additionally, solder, where used for the connecting members 904, may bereflowed in block 122 to affix the second package 902 to the firstpackage 800. In yet other embodiments, the connecting members may besolid material such as copper, gold, or the like, and affixed to themounting studs 502 via a thin coating of solder, solder paste or aconductive adhesive. In some embodiments, the connecting member 904 maybe, for example, copper, which may form a thin oxide layer (not shown)on the surface. In such an embodiment, the size or radius of theconnecting member 904 or the complementary face of the contoured studsurface 802 may be configured to take the oxide formation into accountduring fabrication. Alternatively, the connecting member 904 having theoxide layer may be treated to remove the oxide layer, for example, byway of reduction, cleaning or the like. Additionally, while theconnecting members 904 are described as having, in some embodiments, thethin oxide layer, the mounting studs 502 or other metal surfaces mayalso have or grow a thin oxide layer which may be removed or accountedfor during fabrication.

In some embodiments, the second package 902 may be mounted at a heightwhere the bottom surface of the second package 902 is separated from thetop surface 602 a of the die 602. In one embodiment, the mounting studs502 and connecting members 904 may be formed at a height sufficient tohold the top package separated from the top surface 602 a of the die602.

In another embodiment, the bottom surface of second package 902 may bein direct contact with the top surface 602 a of the die 602, or may havean adhesive, heat transfer compound or heat sink disposed between thesecond package 902 and the top surface 602 a of the die 602. In someembodiments, the contoured stud surface 802 may have a surfacetopography matching the surface topography of a connecting member 904.Thus, the contoured stud surface 802 and the connecting member 904 mayhave complementary shapes. In such an embodiment, the contoured studsurface 802 will accept the connecting member with little, orsubstantially no, deformation of the connecting member 904. Thus, theconnecting member 904 may have a first shape prior to being mounted onthe mounting stud 502, and a second shape after being mounted to themounting stud 502, with the first and second being substantially thesame. Additionally, there will be few, or substantially no, gaps,bubbles or separation in the contact between the contoured stud surface802 and the surface of the connecting member 904.

For example, where the connecting member 904 is a solder ball, thecontoured stud surface 802 may have a complementary hemispherical,concave shape matching the expected surface contour or topography of thesolder ball connecting member 904. Such a contoured stud surface 802increases the contact area between the solder ball connecting member 904and the stud 502, while permitting the solder ball connecting member 904to retain a generally spherical shape without substantial deformation.The solder ball connecting member 904 may be substantially free fromdistortion that may cause the solder ball to enlarge horizontally andcause a short or bridge to an adjoining solder ball. Therefore, a finerbond pitch, or a smaller separation between adjoining connectingmembers, may be achieved. In other embodiments, the mounting stud mayhave a contoured stud surface 802 with a shape corresponding to anotherconnecting member shape, such as an ovoid, cylinder, or the like. Forexample, where a solder bump is used as a connecting member, the solderbump may have a parabolic shape, and the mounting stud 502 may be milledor etched with a parabolic depression to create the contoured studsurface 802.

FIGS. 10 through 15 illustrate cross-sectional views of intermediatesteps in forming of a package-on-package device with contoured mountingstuds according to a second embodiment of the disclosure. In such anembodiment, pre-formed mounting studs 1102 (see FIG. 11) may be attachedto the package lands 202. FIG. 10 illustrates the preparation of thepackage lands 202. While the preparation for the package lands 202 isdescribed here with respect to pre-formed mounting studs 1102, all orpart of the described package land preparation steps may be applied toapplication of the formed mounting studs 502 described above.

Forming the studs 1102 in block 108 may, in some embodiments, furthercomprise preparation of the package lands 202 for pre-formed mountingstuds 1102. For example, a conductive material 1006, such as solderpaste, solder or a conductive adhesive may be applied to the packagelands 202. Additionally, an organic solderability preservative (OSP), orother solder-compatible coating may be applied to the package lands 202prior to applying the pre-formed mounting studs 1102. An anticorrosioncoating such as an OSP may be applied to the pre-formed mounting studs1102, to the package lands 202, or to both. An OSP may be advantageouswhere a first substrate 200 or first package 800 is prepared orassembled prior to mounting a second package 902 (FIG. 9), as the OSPmay protect or preserve the surface of a pre-formed mounting stud 1102or package land 202 that may be prone to corrosion during long termstorage or handling.

Alternatively, a coating resistant to corrosion may be applied to thepre-formed mounting studs 1102, the package lands 202, or both. Forexample, a coating of gold (Au), palladium (Pd), nickel (Ni), alloys ofthe foregoing, or the like may be deposited or electroplated on thepre-formed mounting studs 1102 or the package lands 202 as ananticorrosion coating.

Additionally, a stencil 1002 or other mask may be provided over thefirst substrate 200. The stencil 1002 may, for example, be used in placeof the mask 302 (FIG. 3), and may be removable or reusable. The stencil1002 may also have prepositioned stud openings 402 created in thestencil 1002 to align with the package lands 202.

Pre-formed mounting studs 1102 may be applied in block 108 as shown inFIG. 11. In one embodiment, a spherical pre-formed mounting stud 1102may be placed through the prepositioned stud openings 402.Alternatively, the pre-formed mounting stud 1102 may be cylindrical, oranother useful shape. Spherical pre-formed mounting studs 1102 may beapplied through the stud openings 402 by applying a suitable volume ofspherical mounting studs 1102 over the stencil 1002 and into the studopenings 402.

The mounting studs 1102 may then be bonded to the package lands 202 inblock 112, as shown in FIG. 12. A pre-formed mounting stud 1102 may beattached to the package land 202 by way of the conductive material 1006.The conductive material 1006 may be solder or solder paste, and thebonding may be performed by reflowing the conductive material 1006.

The stencil 1002 may be removed in block 110, and then a die 602 mountedin block 114 and an MUF 702 applied in block 116, as shown in FIG. 13.The pre-formed mounting studs 1102 may be contoured in block 118, asshown in FIG. 14 and a second package 902 mounted to the pre-formedmounting studs 1102 in block 120, as shown in FIG. 15. The contouringand mounting may be substantially the same techniques described abovewith respect to FIGS. 8 and 9.

FIG. 16A illustrates a cross-sectional view of a formed or cylindricalmounting stud 502 with a contoured stud surface 802 while FIG. 16Billustrates a cross-sectional view of a spherical pre-formed mountingstud 1102 having a contoured stud surface 802 according to embodimentsof the disclosure. In one embodiment, the connecting member 904 may havea radius 904 a between about 75 μm and about 165 μm, and a diameterbetween about 150 μm and about 330 μm. In such embodiments, the radius802 a of the hemispherical contoured stud surface 802 will generallymatch that of the connecting member 904, namely between about 75 μm andabout 165 μm. The mounting stud 502 may, in some embodiments, have aheight of about 150 μm, and a radius of about 125 μm, resulting in adiameter of about 250 μm. Similarly, a spherical pre-formed mountingstud 1102 may have a diameter of about 250 μm.

FIG. 17 illustrates a cross-sectional view of embodiments of contouredmounting studs in relation to each other according to an embodiment ofthe disclosure. The bond pitch 1706 may be between about 225 μm and 350μm, and the standoff height between the first package 800 and the secondpackage 902 may be about 200 μm or less. Skilled practitioners willrecognize that the radius 904 a of the connecting member 904 anddiameter of the mounting stud 502 may be adjusted to achieve a desiredbond pitch 1706 and standoff height 1708. Additionally, embodiments ofthe mounting studs 502 according the disclosure may have a jointseparation 1702 as small as about 15 μm to about 200 μm.

Although embodiments of the present disclosure and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. For example, it will be readily understood by those skilled inthe art that many of the features, functions, processes, and materialsdescribed herein may be varied while remaining within the scope of thepresent disclosure. Moreover, the scope of the present application isnot intended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification.

As one of ordinary skill in the art will readily appreciate from thedisclosure of the present disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A device, comprising: a package land disposed ona first side of a substrate; a mounting stud disposed on and inelectrical contact with the package land, the mounting stud having acontoured stud surface having a topography complementary to a topographyof a portion of a surface of a connecting member; and a molded underfill(MUF) disposed at the first side of the substrate and covering at leasta portion of the mounting stud.
 2. The device of claim 1, wherein thecontoured stud surface is substantially hemispherical and configured toaccept a connecting member having a substantially hemispherical surface.3. The device of claim 2, further comprising a connecting member mountedto the mounting stud at the contoured mounting stud surface and having asecond shape, the second shape being substantially the same as a firstshape of the connecting member prior to being mounted on the mountingstud.
 4. The device of claim 2, wherein the contoured stud surface has aradius of between about 75 μm and about 165 μm.
 5. The device of claim2, wherein the mounting stud is substantially spherical.
 6. The deviceof claim 5, wherein the mounting stud is mounted to the package land bysolder.
 7. The device of claim 2, wherein the connecting member issolder.
 8. A device, comprising: a first package having at least aninterposer substrate and a redistribution layer (RDL) at a first side ofthe first package; a plurality of package lands disposed in the RDL, afirst surface of each package land exposed through a first surface ofthe RDL; a plurality of mounting studs, each of the plurality ofmounting studs mounted on one of the plurality of package lands, andeach of the plurality of mounting studs having a contoured stud surface;a second package having a plurality of via lands exposed at a firstsurface of the second package; and a plurality of connecting membershaving a surface complementary to the contoured stud surface, each ofthe plurality of connecting members in contact with the contoured studsurface.
 9. The device of claim 8, further comprising a die disposed onthe first side of the first package, and a molded underfill (MUF)disposed at the first side of the first package, the MUF in contact withat least a portion of each of the plurality of package lands and incontact with at least a portion of the die.
 10. The device of claim 8,wherein the contoured stud surfaces are exposed at a side of the MUF.11. The device of claim 8, wherein a bond pitch of the plurality ofmounting studs is between about 225 μm and 350 μm.
 12. The device ofclaim 8, wherein a standoff height between the first package and thesecond package is 200 μm or less.
 13. A method for forming a device,comprising: providing a first substrate having a package land disposedon a first side; forming a mounting stud on the package land; contouringthe mounting stud by creating a contoured stud surface on the mountingstud and resulting in a first package, the contoured stud surface havinga shape complementary to a shape of a connecting member; and mounting asecond package to the first package by providing the connecting memberand attaching the second package to the connecting member and thecontoured stud surface to the connecting member.
 14. The method of claim13, wherein contouring the mounting stud comprises etching the mountingstud.
 15. The method of claim 13, wherein the contouring the mountingstud comprises forming a substantially hemispherical contoured studsurface.
 16. The method of claim 13, wherein the connecting member issolder with a substantially spherical shape.
 17. The method of claim 13,wherein the forming the mounting stud comprises forming a mask on thefirst side of the first substrate and forming a stud opening in the maskover the package land.
 18. The method of claim 17, wherein the formingthe mounting stud further comprises forming the mounting stud in thestud opening using a deposition process.
 19. The method of claim 17,wherein the forming the mounting stud further comprises: forming themounting stud separate from the first substrate; placed the mountingstud in the stud opening; and attached the mounting stud to the mountingland.
 20. The method of claim 13, wherein the second package is mountedat a standoff height from the first package of 200 μm or less.